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EZ81 - series resistor - first cap in CLCLC filters

Pierre All Messages By This Member #414 Dear All ? I'm going to do my first PSU... tnx for this amazing tool that is PSUD. I am implementing a PSU for an high quality line stage. The load on the PSU will not be more than 40ma and the final B+ should be about 250V. I have several EZ81 around, so that will me my rectifier. The PSU will be a CLCLC. I hope somebody can help with this: ? 1. I read that it's better to put a resistor in series with the EZ81 between the secondary and the tube, what do you think? Any experience with that? ? 2.? I was told that it's best to have the first cap really small, something below 15uF. I saw cases where people use a first cap of 47uF and cases where people use 1uF... what's the sonic difference?? I tried to simulate both, of course I get different ripple and mostly different rise time.? ? I'm interested in sound, do these choice impact sound significantly?? ? I hope somebody is willing to help ? Best Wishes to all Pierre ?
Richard D All Messages By This Member #415 Pierre, Mullard specifies a maximum capacitor value of 50uF, and a minimum 230R limiting resistance in series with each anode (which includes the winding resistance). Bear in mind that this is specified at maximum voltage and current, which you are nowhere near. The usual thing is to use a 47uF capacitor and add whatever resistance (if any) you need to give the voltage you want.
Craig Sawyers All Messages By This Member #416 Have you looked at the EZ81 spec sheet and understood it? Craig toggle quoted message Show quoted text ------ Original Message ------ From "Pierre via groups.io" <grammophonia@...> To [email protected] Date 04/04/2025 17:24:37 Subject [duncanampspsud] EZ81 - series resistor - first cap in CLCLC filters Dear All ? I'm going to do my first PSU... tnx for this amazing tool that is PSUD. I am implementing a PSU for an high quality line stage. The load on the PSU will not be more than 40ma and the final B+ should be about 250V. I have several EZ81 around, so that will me my rectifier. The PSU will be a CLCLC. I hope somebody can help with this: ? 1. I read that it's better to put a resistor in series with the EZ81 between the secondary and the tube, what do you think? Any experience with that? ? 2.? I was told that it's best to have the first cap really small, something below 15uF. I saw cases where people use a first cap of 47uF and cases where people use 1uF... what's the sonic difference?? I tried to simulate both, of course I get different ripple and mostly different rise time.? ? I'm interested in sound, do these choice impact sound significantly?? ? I hope somebody is willing to help ? Best Wishes to all Pierre ?
Duncan Munro All Messages By This Member #417 Hi Pierre, ? Yes please put a resistor in place as per data sheet advice as this will limit surge/peak current and extend the life of the tube cathode I'd use 47uF if I was just using a C filter or CRC as that will be the optimum value. However... as you are using CLCLC, it's a specific circumstance that might benefit from a smaller value. If you have C1 L1 C2 L2 C3, it's good for C1 < C2 and C2 < C3 as this will help to prevent ringing in the system Some tips that might help you with all of this: ? You can simulate the anode resistor by working out the source impedance using one of the transformer calculators, then simply add the value of a single anode resistor to this value. For example if you have calculated 110 ohms source impedance and have a 230 ohm protection resistor for each anode, use 110+230 = 340 ohms Check out the tube data as advised by others, my TDSL site has links to data sheets which you may find useful Check the peak current in the rectifier and compare with the data sheet. Try different capacitor values and you can see the effect of changing the value. Lower peaks are likely to translate into longer tube life Experiment with a smaller capacitor value at the start of the filter chain, it's really easy to try different ideas with PSUD to get to where you need quickly, look at the effects on filter ringing If your filter is left with a small amount of ringing, use the soft start feature in PSUD to simulate that the tube conduction will slowly rise; that should make it go away Sonic differences will always be subjective, and for that reason it's a topic I generally avoid, however you may want to consider a couple of items: Lower ripple is generally better. Single ended amps will end up with ripple in the output so less ripple will translate to less hum out of the speaker. Push-pull amps should cancel the hum, however they will be affected by intermodulation distortion so they still benefit from lower ripple. As your target is a line stage, this would be treated the same as single ended Power supply impedance - there are two things to consider, one is "sag" from the power supply which is where it runs out of steam at high load and the voltage will reduce, potentially resulting in quieter periods after transients. The other is the impedance to AC variations in the load which can affect the sound output at different frequencies. PSUD will check for sag; the stepped current load is great for assisting with this. It doesn't currently allow for output impedance vs. frequency to be plotted Hope the above is of some help to you. ? Regards, Duncan

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